Stool guaiac test
Colon cancer - guaiac test; Colorectal cancer - guaiac test; gFOBT; Guaiac smear test; Fecal occult blood test - guaiac smear; Stool occult blood test - guaiac smearThe stool guaiac test looks for hidden (occult) blood in a stool sample. It can find blood even if you cannot see it yourself. It is a common type of fecal occult blood test (FOBT).
Guaiac is a substance from a plant that is used to coat the FOBT test cards to make them able to detect blood.
How the Test is Performed
Usually, you collect a small sample of stool at home. Sometimes, your health care provider may collect a small amount of stool from you during a rectal examination.
If the test is done at home, you will use a test kit. Follow the kit instructions exactly. This ensures accurate results. In brief:
- You collect a stool sample from 3 different bowel movements.
- For each bowel movement, you smear a small amount of the stool on a card provided in the kit.
- You mail the card to a laboratory for testing.
Be sure to keep the stool away from any urine. Mixing of urine and stool can spoil the sample.
How to Prepare for the Test
Some foods can affect test results. Follow instructions about not eating certain foods before the test. These may include:
- Red meat
- Cantaloupe
- Uncooked broccoli
- Turnip
- Radish
- Horseradish
Some medicines may interfere with the test. These include vitamin C, aspirin, and NSAIDs such as ibuprofen and naproxen. Ask your provider if you need to stop taking these before the test. Never stop or change your medicine without first talking to your provider.
How the Test will Feel
The at-home test involves a normal bowel movement. There is no discomfort.
You may have some discomfort if the stool is collected during a rectal exam.
Why the Test is Performed
This test detects blood in the digestive tract. It may be done if:
- You are being screened or tested for colon cancer.
Colon cancer
Colorectal cancer is cancer that starts in the large intestine (colon) or the rectum (end of the colon). It is also sometimes simply called colon ca...
ImageRead Article Now Book Mark Article - You have abdominal pain, changes in bowel movements, or weight loss.
- You have anemia (low blood count).
Anemia
Anemia is a condition in which the body does not have enough healthy red blood cells. Red blood cells provide oxygen to body tissues. Different type...
ImageRead Article Now Book Mark Article - You say you have blood in the stool or black, tarry stools.
Normal Results
A negative test result means that there is no blood in the stool. Occasionally, this test will miss very small amounts of blood in the stool that is below the level of detection of this test (false negative).
What Abnormal Results Mean
Abnormal results may be due to problems that cause bleeding in the stomach or intestinal tract, including:
- Colon cancer or other gastrointestinal tumors
Tumors
A tumor is an abnormal growth of body tissue. Tumors can be cancerous (malignant) or noncancerous (benign).
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Colon polyps
Colon polyps
A colorectal polyp is a growth on the lining of the colon or rectum.
ImageRead Article Now Book Mark Article - Bleeding veins in the esophagus or stomach (esophageal varices and portal hypertensive gastropathy)
Esophageal varices
The esophagus (food pipe) is the tube that connects your throat to your stomach. Varices are enlarged veins that may be found in the esophagus in pe...
ImageRead Article Now Book Mark Article - Inflammation of the esophagus (esophagitis)
Esophagitis
Esophagitis is a condition in which the lining of the esophagus becomes swollen, inflamed, or irritated. The esophagus is the tube that leads from y...
ImageRead Article Now Book Mark Article - Inflammation of the stomach (gastritis)
Gastritis
Gastritis occurs when the lining of the stomach becomes inflamed or swollen. Gastritis may last for only a short time (acute gastritis) or it may lin...
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Hemorrhoids
Hemorrhoids
Hemorrhoids are swollen veins in the anus or lower part of the rectum.
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Crohn disease or ulcerative colitis
Crohn disease
Crohn disease is a disease where parts of the digestive tract become inflamed. It most often involves the lower end of the small intestine and the be...
ImageRead Article Now Book Mark ArticleUlcerative colitis
Ulcerative colitis is a condition in which the lining of the large intestine (colon) and rectum become inflamed. It is a form of inflammatory bowel ...
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Peptic ulcer
Peptic ulcer
A peptic ulcer is an open sore or raw area in the lining of the stomach or intestine. There are two types of peptic ulcers:Gastric ulcer -- occurs in...
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Other causes of a positive test may include:
- Nosebleed
- Coughing up blood and then swallowing it
If the stool guaiac results come back positive for blood in the stool, your provider will likely recommend other tests, often including a colonoscopy.
Colonoscopy
A colonoscopy is an exam that views the inside of the colon (large intestine) and rectum, using a tool called a colonoscope. The colonoscope has a sm...
The stool guaiac test does not diagnose cancer. Screening tests such as colonoscopy can help detect cancer. The stool guaiac test and other screenings can catch colon cancer early, when it is easier to treat.
Risks
There can be false-positive and false-negative results.
Errors are reduced when you follow instructions during collection and avoid certain foods and medicines.
References
National Cancer Institute website. Colorectal cancer prevention (PDQ) - health professional version. www.cancer.gov/types/colorectal/hp/colorectal-prevention-pdq. Updated March 28, 2024. Accessed April 22, 2024.
National Comprehensive Cancer Network website. NCCN clinical practice guidelines in oncology (NCCN guidelines): colorectal cancer screening. Version 1.2024 - February 27, 2027. www.nccn.org/professionals/physician_gls/pdf/colorectal_screening.pdf. Accessed April 22, 2024.
Patel SG, May FP, Anderson JC, et al. Updates on age to start and stop colorectal cancer screening: recommendations from the U.S. Multi-Society Task Force on colorectal cancer. Gastroenterology. 2022;162(1):285-299. PMID: 34794816 pubmed.ncbi.nlm.nih.gov/34794816/.
Savides TJ, Jensen DM. Gastrointestinal bleeding. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 20.
US Preventive Services Task Force website. Final recommendation statement. Colorectal cancer: screening. www.uspreventiveservicestaskforce.org/uspstf/recommendation/colorectal-cancer-screening. Published May 18, 2021. Accessed February 11, 2024.
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Fecal occult blood test - illustration
A fecal occult blood test is a noninvasive test that detects the presence of hidden blood in the stool. Blood in the stool that is not visible is often the first, and in many cases the only, warning sign that a person has colorectal disease, including colon cancer.
Fecal occult blood test
illustration
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Fecal occult blood test - illustration
A fecal occult blood test is a noninvasive test that detects the presence of hidden blood in the stool. Blood in the stool that is not visible is often the first, and in many cases the only, warning sign that a person has colorectal disease, including colon cancer.
Fecal occult blood test
illustration
Review Date: 1/30/2023
Reviewed By: Michael M. Phillips, MD, Emeritus Professor of Medicine, The George Washington University School of Medicine, Washington, DC. Internal review and update on 02/10/2024 by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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